1. Field of the Invention
This invention relates to the compatibilization of fillers with polyolefin resins. More particularly, this invention relates to a method for rendering acid reactable inorganic mineral fillers more compatible with polyethylene resins to improve the physical properties of the resins.
2. The Prior Art
In the manufacture of canned foodstuffs, the containers, usually metal cans, are filled with the foodstuff, covered with a metal end closure and sealed. One of the disadvantages of canning foodstuffs in metal containers is that the presence of the food product may cause the interior of the can to corrode, the corrosion products of which contaminate the food product.
Attempts to substitute certain inert synthetic resin materials such as polyethylene for metal in the canning of foodstuffs have encountered the disadvantage that the sidewalls of containers fabricated from such resins generally do not have acceptable stiffness and rigidity to withstand buckling from loading stresses encountered when the containers are stacked during storage.
The art has devised a number of ways to increase the stiffness of polyethylene and other polyolefin resins. Included in these methods is to incorporate in the polyolefin resin a filler material such as wood flour and inorganic mineral fillers such as metal carbonates, clay or mica, e.g., U.S. Pat. No. 3,463,350, Br. No. 905,069 and U.S. Pat. No. 3,668,038.
Containers molded from filled polyolefin resins generally have poor impact strength and crack when dropped from relatively low (e.g., 2 feet or less) heights.
The poor impact properties of the container sidewalls are believed due to the poor compatibility of the fillers and the polyolefin matrix.
Various means are known to the art for improving the compatibility of fillers with polyolefin resins which involve modification of the filler surface. For example, British Patent No. 905,069 teaches that polyethylene resins filled with fatty acid coated metal carbonates exhibit improved stress cracking resistance when compared with polyethylene filled with uncoated metal carbonates. U.S. Pat. No. 3,084,117 teaches improving the compatibility of clays by base-exchanging clay particles with an unsaturated organic nitrogen compound to form an organoclay adduct which is admixed with a polyolefin resin and the admixture subjected to high energy ionizing radiation to cross-link the unsaturated nitrogen compound.
The prior art methods discussed above either do not provide the improvement demanded in container applications of the polyolefin resin or the compatibilization technique deleteriously induces undesirable physical properties in the resin otherwise acceptable.